Ciro Immobile's hat trick in Lazio's 4-1 win over big-spending AC Milan was the work of a complete forward showing off all of the weapons in his arsenal.

The Italy striker rounded off his sterling performance Sunday by providing the assist when Luis Alberto finished off a swift counterattack.

"It's not often that you score three goals against Milan," Immobile said. "And Lazio showed that it can compete with the strongest squads."

The last time Lazio scored four goals in a Serie A match against Milan came in 1999-2000, when the Roman side won its second Italian league title.

Immobile has had quite a start to the season.

After scoring eight goals in six preseason friendlies, he now has six in Lazio's opening four matches, including two in a 3-2 win over Juventus in the Italian Super Cup.

Immobile also scored for Italy in a 1-0 win over Israel in World Cup qualifying last week.

He's displaying the same form that helped him lead Serie A with 22 goals in 33 matches for Torino in 2013-14.

"It would be great to do that again," Immobile said. "It's useless denying that (the goalscoring chart) is the most important standings for a striker."

The 27-year-old Immobile appeared on the cusp of greatness after his breakout season at Torino. But he followed that with an unsuccessful year with Borussia Dortmund in the Bundesliga and a short loan spell at Sevilla in Spain before returning to Torino.

It was Zdenek Zeman, the veteran Czech coach who employs an all-out attacking style, who first capitalized on Immobile's potential en route to the Serie B title with Pescara in 2011-12.

On a memorable squad that also featured current Italy teammates Marco Verratti and Lorenzo Insigne, Immobile scored 28 goals in 37 matches.

He joined Lazio last season and scored 23 goals to improve on his personal single-season record in the top division.

It's been quite a journey for a player who came up through Juventus' youth system but never really got the chance to prove himself with the Turin power.

"I'm happy at Lazio. This is a serious squad made up of magnificent people and we all work well together," Immobile said. "I've matured here and I feel like I'm a part of something. I want to continue like this."

Especially in a season which culminates with the World Cup in Russia.

Against Milan, Immobile made celebrated defender Leonardo Bonucci look like an amateur.

For his second goal, Bonucci moved for an instant to mark Luis Alberto and that was all the space Immobile needed to score by the far post.

Bonucci was also partly responsible for Lazio's third goal as he narrowly missed intercepting a cross, again providing Immobile room.

"We lost our focus the first time they had a chance," Bonucci said of remodeled Milan, which spent more than 200 million euros (nearly $250 million) in the transfer market, including his own move from Juventus.

"They're united and we're still lacking that," Bonucci added. "The defensive phase has to be a collective effort. It was utopia to think everything could work perfectly already."

Milan had opened the season with six straight wins between the Europa League and Serie A.

"We still need to become a squad," Milan coach Vincenzo Montella said. "This match tells us that we're behind. We've got players who have trained together only three or four times."

Lazio, meanwhile, is in fourth place, two points behind leaders Juventus, Napoli and Inter Milan, and on course for a Champions League spot.

Up next for Immobile: Lazio's visit to Dutch side Vitesse in the Europa League on Thursday.